Effect of optical penetration on laser generatedthermoelastic ultrasound in solids

I.IntroductionTbegenerationofu1trasoundbytheirradiationofpulsedlaseratso1idsurfacehasbeenwidelystlldied,boththeorctica1lyandexpcrimentallyI1-8].Intheprocessoflaserthermoelasticg6nerationofu1trasound,temperatureriseinduccdbytheabsorptionoflaserenergyproducestherma1expansion,andthcnanultrasonicsourceiscreated.Sofar,thestudyof1asergenera-honofultrasoundinso1idsconcentratesmain1yonmeta1s,anduntilrecent1y,1ittleattentionhasbenpaidtonon-mctals.Inametal,1aserenergyisabsorbedonlyatthesurfaceofthesamp…

Effect of optical penetration on laser generated thermoelastic ultrasound in solids

The effect of optical penetration on laser thermoelastically-generated ultrasound in non-metallic solids is studied theoretically on the basis of the thermoelastie equations. In one-dimensional model, on the assumption of some finite laser penetration, the general expression of wave displacement is obtaincd by solving the thermal diffusion and thermoelastic displacement equations, from which the influencc of optical absorption on the displacement amplitude is analyzed. In the case of two-dimensional axial symmetry, on neglecting the thermal diffusion, we solve the thermoelastic wave equation by means of the integral transform method and obtain analytic expressions of the wave displacement components in the far-field.Directivily patterns of both longitudinal and shear waves are presented and discussed.